1. Field of the Invention
The present invention relates to a device for monitoring a sheet material in a conveying apparatus which is used in the field of photographic technology and which conveys sheet materials such as heat-sensitive materials and photosensitive materials e.g., photographic films and photographic paper, along a prescribed conveying path, and to a method for monitoring a sheet material by using the device.
2. Description of the Related Art
Conventionally, when sheet materials, for example, photosensitive materials such as photographic films, are conveyed along a prescribed conveying path, a combination of an infrared LED and a phototransistor (hereinafter, this combination is referred to as a "photosensor") is provided for each film size (film width), such that respective photosensors are disposed at positions corresponding to the edges of films of the various film sizes. The size of the film being conveyed is recognized by the detection of the film edge by the photosensor.
The film size can be recognized by using this method. However, when a film meanders, the phototransistor disposed at a position next to the "correct" position may detect the edge of the film such that a size different from the correct size is recognized.
The above problem occurs because the photosensors are not continuously arranged but are disposed at discrete positions along the edge-line of films. An increased number of phototransistors may be disposed without gaps therebetween to overcome this problem.
However, even when an increased number of phototransistors are disposed without gaps therebetween, the detection points which are detected by the phototransistors still remain as discrete points due to restrictions imposed by the shape of the phototransistor. Therefore, errors in recognition of film size cannot be eliminated completely.